#include <stdio.h>

#define SIZE 21

int main()
{
    float a[SIZE] = {0};
    scanf("%f", a);
    int i;
    for (i = 1; i <= SIZE; i++)
    {
        a[i] = 2*a[i-1] - 3;
    }
    printf("%.2f\n", *(a+SIZE-1));
}